The current grant focuses upon studies of aberrant DNA methylation patterns in human cancer cells. Specifically, we are exploring the causes and consequences of regional increases in DNA methylation in transformed cells. These changes may mark and/or contribute to the chromosome structural alterations underlying abnormal gene expression events important for the initiation and/or progression of human tumors. The short arm of chromosome 11 appears to be a "hot spot" for DNA hypermethylation which could contribute to loss of gene expression. Current studies are examining whether such changes also exist in other genomic areas specifically involved in the pathogenesis of individual human cancers. Temperature sensitive viruses are being used to delineate the precise timing of the increased methylation following cell transformation. Gene insertion studies will be used to examine transformation effects upon specific regions of DNA. Finally, a model for increased cellular DNA methylating capacity has been constructed to study the resultant molecular changes and the phenotypic consequences for eukaryotic cells.